Preheat oven to 450 degrees F.
Put beef, fat side up, in a shallow flameproof roasting pan. Sprinkle salt and pepper over top. Roast beef in lower third of oven for 20 minutes. Reduce oven temperature to 350 degrees F. and roast beef 1 hour and 15 minutes more or until a meat thermometer inserted 2 inches into center of meat registers 115 degrees F. Transfer beef to a cutting board, reserving pan juices in pan and let stand 25 minutes. For vegetables: In a large skillet, cook onions in 1 1/2 tablespoons oil over moderately low heat, stirring occasionally, until softened and golden, about 8 minutes. With a slotted spoon, transfer onions to a bowl and cook carrots and celery in remaining tablespoon oil over moderate heat, stirring until crisp-tender. Add mushrooms and cook, stirring, until liquid released from mushrooms evaporates. Transfer vegetables to a bowl and season with salt and pepper.
While beef rests, skim fat from pan juices and reserve 4 tablespoons of fat for Yorkshire puddings. (Puddings may be baked while beef is standing.) Place roasting pan on stovetop. Add wine to roasting pan and simmer over moderately high heat, scraping up any brown bits, until reduced to about 1/2 cup. Add demi-glace, jelly, horseradish, vegetables, parsley, and salt and pepper to taste and simmer, stirring occasionally, until heated through. Discard string and, with a sharp knife, remove rib bones. Thinly slice beef and serve over Yorkshire puddings with gravy.
*available at specialty foods shops.
In a blender blend flour, salt, eggs and milk until just smooth. Chill batter, covered, 30 minutes. Preheat oven to 425 degrees F. Arrange four 5 1/2-inch pie plates in a large shallow baking pan and spoon 1 tablespoon beef fat into each. Put baking pan in middle of oven for 5 minutes to heat oil. Quickly pour 1/2 cup batter into each pie plate and bake in the middle of oven until puddings are puffed and golden brown, about 18 minutes. With tongs, remove puddings from pie plates and serve immediately.;
Recipe courtesy of Gourmet Magazine for Sara Moulton on Cooking Live